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I know my question is stupid, it is stupid because I am not understanding it correctly.

I thought two of following is required to calculate watts. Voltage, Current or Resistance/(Impedance in AC) is required.

The only way to get current is when we have a load. How does power plant generate in unit of watts when where is no load.

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  • \$\begingroup\$ I guess the direct answer is there is load - the grid and the consumers. The next right thing to ask would be "what happens if a running generator is suddenly disconnected from the grid?" \$\endgroup\$ – sharptooth Apr 6 '15 at 15:33
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    \$\begingroup\$ Where did you get the idea that a power plant would generate anything when there is no load? \$\endgroup\$ – Wouter van Ooijen Apr 6 '15 at 15:36
  • \$\begingroup\$ I didn't claim that a power plant would generate "anything". I said How is it generating or why is units in watts. \$\endgroup\$ – user206168 Apr 6 '15 at 15:39
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    \$\begingroup\$ "How does power plant generate in unit of watts when where is no load." : when there is no load the plant does not generate anything. \$\endgroup\$ – Wouter van Ooijen Apr 6 '15 at 19:01
  • \$\begingroup\$ @sharptooth: The answer to that question is "nothing good happens". You might be entertained by this: blogs.msdn.com/b/ericlippert/archive/2011/01/10/… \$\endgroup\$ – Eric Lippert Apr 6 '15 at 22:11
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If there's no load, and it's disconnected, it can't really be said to "generate" any power. No current = Zero watts. Mechanical work will be wasted spinning the generator shafts.

Some generators (e.g. small wind systems) have "dump" loads that can be switched in if there is no real load, in order to avoid the generator accelerating beyond its design limits.

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  • \$\begingroup\$ so above answer make sense? and all the voltage has to be used or it is wasted if it is not used in real time? \$\endgroup\$ – user206168 Apr 6 '15 at 15:51
  • \$\begingroup\$ Yes, electrical power from a generator is wasted if not used in real time. \$\endgroup\$ – pjc50 Apr 6 '15 at 15:58
  • \$\begingroup\$ I wish I can give you thumbs up, not qualified. what about the load in AC 3 phase? is impedance same thing as load or resistance? \$\endgroup\$ – user206168 Apr 6 '15 at 16:01
  • \$\begingroup\$ also to understand it better. Power Plant generator has limit for voltage generation correct? \$\endgroup\$ – user206168 Apr 6 '15 at 16:03
  • \$\begingroup\$ "Load" is a non-precise term for anything that consumes energy. "Resistance" is ohmic behaviour. Impedance has the same units as resistance and similar effects but is frequency-dependent and not ohmic. Generators have a design safe limit but may briefly produce very high voltages if spun without a load. \$\endgroup\$ – pjc50 Apr 6 '15 at 16:05
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A power plant will produce only voltage if there is no load, however, it will be able to deliver current if a load is connected, and demands current (or power).

A power plant or generator will be rated for the maximum power it can deliver, but only produces that amount of power if a load requires it.

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  • \$\begingroup\$ @Peter: Your first sentence doesn't read the way you intended. Try If there is no load a power plant will <del>only</del> produce voltage only. \$\endgroup\$ – Transistor Jan 30 '16 at 12:35
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A power plant is like a water pump. It generates a pressure (voltage) between its flanges, but water (current) can only flow when the flanges are connected.

If you connect them via a thin pipe (small load / small resistor), water will flow, but the flow is limited by the friction inside the pipe.

With a wider pipe, more water flows.

As long as the pump is strong enough, it will maintain the pressure1). However, if your pipe is too wide, the pressure between the pipes will be smaller than nominal.

Pressure difference times flow is power2), so if there is pressure (voltage) but no flow (current), no power is consumed/produced. Little flow means little power. The pump (plant) only generates the demanded power. A label of 1000W just indicates the maximum output, i.e. the strength. So, nothing is wasted.

(OK, in reality, there are some difficulties. You can not switch on/ off power plants as fast as you need / don't need power, but that's nothing to care about when trying to understand the principles of electricity)


1)This is not true for most pumps in reality, but it describes quite well what happens

2) Here, power = energy / time, i.e. wattage etc.

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Mr Alessandro Volta, during some chemical experiments didn’t like the unbalance in electron between two plates, and connect a wire to transfer the excess of electrons from one plate to the plate that today we call anode.

During this transfer, the wire becomes hot. The next day he decide to cut the wire and put something in between to use this work (the heat) to do something for him….and this was the start of a big change of our world!

No matter if this is DC or AC

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  • \$\begingroup\$ This answer does not address the primary question, "How does power plant generate in unit of watts when where is no load." \$\endgroup\$ – Transistor Jan 30 '16 at 12:32
  • \$\begingroup\$ @transistor It is if you dig more....this forum it is not for installation electricians only \$\endgroup\$ – GR Tech Jan 31 '16 at 15:06
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During supplying current, motors starts to rotate, like that during the mechanical rotation of motors it creates change in flux, thus potential create that leads to voltage. This is the principle for alternator. Watts is only to calculate power consumption or power production. Current is produce during the flow of electron by potential.

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